Conventional commercial elevators travel in an elevator shaft between two elevator rails and therefore require a shaft of precise dimensions. Requiring a precision shaft to carry two rails, each on an opposing wall, is not an obstacle in the commercial market since commercial construction standards are generally more exacting. Typical commercial elevator rails have a "T" shape with the vertical base of the "T" extending into the shaft. The elevator cab is then attached to the rails with rail guides, rollers, or a slide mechanism made, for example, from a TEFLON-type product. An example of a hydraulic elevator that travels between two T-shaped elevator rails in a shaft is disclosed in U.S. Pat. No. 3,968,860 to Atkey.
The conventional residential elevator, on the other hand, typically travels on a set of commercial T-shaped elevator rails which are disposed on the same wall of the elevator shaft. By placing both rails on which the elevator travels on one shaft wall, a home elevator does not demand precise shaft dimensions. Instead of using a slide mechanism, however, known residential elevators use sets of specially hardened polyurethane-type rollers which have internal bearings. Unfortunately, the commercial T-shaped rails are quite expensive to make and are costly to ship. In addition, the commercial rails are often tedious to align in a home environment. The multiple rollers used by residential elevators also increase the cost.
Besides the problems associated with T-shaped elevator rails, two other characteristics of conventional home elevators also present serious handicaps. The first, is the mounting of a sheave or other lifting aid above the uppermost end of the pair of elevator rails. For example, U.S. Pat. No. 4,664,230 to Olsen illustrates a residential elevator with its power unit and associated lifting gear permanently mounted on the uppermost end of a pair of elevator rails above the cab of the elevator. Thus, a home whose upper story does not have clearance for both an elevator cab and a sheave or other motor assembly mounted above the elevator cab would be unable to accommodate such a residential elevator.
The second detrimental characteristic of residential elevators involves the practice of burying the piston assembly for an elevator's hydraulic jack. For example, U.S. Pat. No. 5,020,641, to Olsen et al., and U.S. Pat. No. 3,968,860, to Atkey, both illustrate the burial of their respective hydraulic cylinders. As shown in both patents, for every foot the elevator travels up, there must be a corresponding foot for the piston to travel down. Because the elevator cab rides on the piston, there is no need for a sheave or motor assembly on the uppermost ends of the pair of elevator rails. However, prior to installation of the elevator, a hole must be drilled to accept a hydraulic chamber and piston. The drilling process adds to installation costs and time, and is particularly difficult where rock or coral must be penetrated.